In timed sports races or competitions, and in particular athletics races, the timing device is generally started in a synchronised manner with the emission of an acoustic signal, and stopped for each competitor when each competitor respectively crosses the finish line. It may happen however that the resolution of the timing system, for example typically a hundredth of a second, is insufficient to distinguish between two competitors whose measured time is identical. To achieve this, auxiliary devices are required to assist timing and there are manually operated systems for this purpose which are based on the visual recognition of images taken in sequence by a high definition camera very precisely centred on the finish line. An operator analyses, in an asynchronous manner after the competitors have finished the race, the sequence of images taken at given times and consequently corresponding to a measured time; this analysis therefore makes it possible to determine a more accurate line crossing time for each competitor, for example to a thousandth of a second, and to rank the competitors in a reliable manner. This type of auxiliary timing display is usually called a “photo finish” device.
This type of auxiliary display system, known for a relatively long time, is disclosed for example in U.S. Pat. No. 3,502,009 relating to a dog race. The photo finish device enables time values, obtained using a first lens centred on a timing device, to be superimposed on images of the competitors using a second lens centred on the finish line. The developed film thus makes it possible to determine the first dog to cross the line and its lap or finish time.
To overcome the problem of competitors masking each other, which may prevent the operator performing a pertinent analysis of the sequence of images around the disputed measured time, photo finish systems very often use several cameras. However, because of the precise alignment required on the finish line, none of the cameras used can be shifted laterally to resolve this masking problem; this is why the two cameras employed are respectively located on either side of the finish line.
There are also known stereoscopic optical systems for the display of three dimensional images, which provide a more user-friendly and intuitive rendering for the person viewing the images. These stereoscopic systems are based on the construction of an image in relief in the same manner as the brain, i.e. from the analysis of two plane images taken along distinct axes of view. These stereoscopic systems thus typically use dual lens cameras, the space between the lenses corresponding, for example, to the mean interocular space, namely around 75 to 80 millimeters. However, these optical systems are unfortunately unsuitable for a photo finish system because of the lateral offset that is required between the photograph shooting axes, which cannot be simultaneously aligned on the finish line and therefore there is no possibility of these systems overcoming the shortcomings of the timing system in a reliable and accurate manner.
There is consequently a need for auxiliary timing systems which are free of these known limitations.